Composite nickel electroplate



H. BROWN 3,090,733

May 21, 1963 COMPOSITE NICKEL ELECTROPLATE Filed April 17, 1961 Cogf'jza (d) 6.7 77.7427@ {aaai-0.2 mi?) l /'e/ cz!l H7, irai?, 277, ffy, efe.)

LM \j /v/ 72.42% c INVENTOR. /Vewr ,Efzaw United States Patent O 3,090,733 COMPOSITE NICKEL ELECTRGPLATE Henry Brown, Huntington Woods, Mich., assignor to The Udylite Research Corporation, Detroit, Mich., a corporation of Michigan Filed Apr. 17, 1961, Ser. No. 103,296 19 Claims. (Cl. 20d-40) This invention relates to an improved composite electroplate on a lmetal base comprising three types of nickel electroplates which are adjacent `or contiguous to each other, and to the method of preparing this composite coating. Such a composite coating provides greatly improved outdoor corrosion protection to underlying basis metals which are susceptible to atmospheric corrosion such as steel, `copper and its alloys, Zinc and its alloys, aluminum and its alloys, magnesium and its alloys, etc.

The composite electropl-ate of this invention comprises three adjacent, bonded layers of nickel having certain thicknesses and in which the intermediate layer of nickel has a higher sulfur content than the nickel layers ywhich sandwich it. Moreover, the upper layer, for optimum results, should have an appreciably higher `sulfur content than the lower layer of nickel underneath the intermediate layer. The lower nickel layer should contain from zero to -a maximum of 0.03% sulfur, and have a thickness of about 0.15 to 1.5 mils, and this thickness would include any nickel or cobalt or nickel alloy strike plates such as nickel-cobalt, nickel-iron or 'nickel-cobalt-iron. The intermediate nickel layer should contain more than about 0.05% sulfur and must contain more sulfur than the top nickel layer. In gener-al it should contain from about 0.05% to about 0.3% sulfur. The thickness of the intermediate layer should be from about 0.005 to about 0.2 mil. The upper nickel layer should contain about 0.02% to about 0.15% sulfur and have a thickness of about 0.15 to 1.5 mils. When the upper nickel layer has only 0.02% or 0.03% sulfur ythen the intermediate layer may have as low as 0.05% sulfur, but when the upper nickel layer contains 0.04% to 0.07% sulfur then the intermediate nickel layer should `contain at least 0.08% sulfur. In general it is preferred that the intermediate nickel layer contain about 0.02% to about 0.1% more sulfur than the upper nickel when the upper layer is a bright nickel containing 0.02 to 0.08% sulfur, and the lower nickel is ya semibright sulfur-free (less than about 0.005% sulfur) nickel. Under such conditions this essentially three layered nickel deposit with an overlying thin bright chromium plate provides considerably improved `outdoor corrosion protection to the basis metal especially in a marine or saline atmosphere (Where salt is used to de-ice streets in winter) than does an equal total thickness of nickel of either the lower layer nickel or the upper layer nickel or a double layer of these two nickels, with the same iinal thin chromium plate. This marked increase in corrosion protection is clearly shown in the now Well established accelerated corrosion tests, the `CASS ,and Corrodkote tests, Iwhich tests are described in Plating vol. 44, p. 763, 1957, Where the improvements obtained in corrosion protection of for example steel `or `copper plated zinc die-castings are usually at least double, when the thin intermediate plate of this invention is used.

It was further found that the luse of the above described intermediate layer of nickel having a relative-ly higher sulfur content than the layers of nickel which sandwich it, made possible tar better corrosion protection to 'the basis metal, for example, steel, and copper plated zinc die-castings than when other intermediate layers were used such as cobalt or tin. With cobalt 'as the intermediate layer, blisters resulted when the corrosion pit reached the cobalt layer and proceeded laterally at a very rapid rate thus Ice lifting the top nickel deposit around the corrosion pit to yform an 4objectionably large blister. With the use of an intermediate layer of tin, the 'adhesion between the two nickel layers was greatly decreased. Other intermediate coatings such as zine or copper have already been proved to be detrimental, with the zinc causing excessive blistering and with copper causing staining and also decreased corrosion resistance.

FIGURES 1-3 are diagrams which illustrate the mechanism rby which the Itri-nickel plate of this invention diverts the corrosion from the basis metal. 'Iihese diagrams show the progression of a vcorrosion pit in a preferred example or" a bright chromium plated composite of the three-layered nickel coating Iwhen exposed to sali-ne or Vacidic ysaline atmospheres or to the CASS or Corrodkote :corrosion tests. In FIG. 1, the usual type of hemispherical corrosion pit Istarting from a pore (a) in the uppermost bright chromium plate is shown penetrating down into the upper bright nickel plate. In FIG. 2, the corrosion pit has 'become a dat bottom pit practically stopping at the lower nickel layer of low sulfur content, `and going laterally in the upper and intermediate nickel layers. Also a certain degree of preferential lateral corrosion is proceeding in the intermediate nickel layer B which has a higher sulfur content than the upper nickel layer A and an even lmore appreciably higher sulfur content than the lower nickel layer C. In FIG. 3, the corrosion pit has widened further without penetrating appreciably into the lower nickel layer C. This is the important consequence of the progression of corrosion with this tri-nickel plate under continued severe exposure conditions. That is, unsightly r-ust spots do not readily occur when the base metal is steel, nor white corrosion ibl-isters when the bas-e metal is copper or bass plated `zinc alloy die castings, or when the base rnetal is aluminumm `or magnesium or alloys thereof. The important fact is that lboth nickel layers A and B continue to corrode, with intermediate layer B corroding somewhat faster than A, but not in complete preference to A, and thus the maximum protection to nickel layer C is obtained, which in turn .protects the more vulnerable -basis metal.

The three-layered nickel composite may be made With dull Watts nickel as the lower layer, and lbright nickel or even a semi-blight nickel or dull nickel as the upper layer providing the upper nickel lay erhas, as already specified, higher sulfur content than the bottom layer. The methods of obtaining the higher sulfur content will be described hereinafter. Improved corrosion protection is obtained even in the absence of a final chromium plate. A preferred form of this invention includes the three-layered nickel plate in which the upper nickel is a bright nickel finish with a final overlying bright chromiuml plate of about 0.005 mil to 0.2 mil thick, and in this form is excellently suited for use on the exterior hardware and trim of automobiles and boats. For these applications, for example, 'bumpers of automobiles, door handles, housing for lights, etc., the basis metal, such as steel, copper, brass, aluminum or zinc die castings after rst plating with copper, brass or chromium, or nickel strikes can then be plated with the three-layered nickel composite las follows: A semi-bright sulfur-free nickel plate in a thickness of about 0.7 to 1.5 mils is first applied and then covered with an intermediate plate of about 0.005 to 0.1 mil nickel having a sulfur content of about 0.08 to about 0.18%, which is then overlaid with a bright nickel plate of about 0.5 to 1 mil thickness from a bright nickel bath that produces about 0.02 to 0.07% sulfur in the deposit, and this upper nickel layer is then covered with a nal thin bright chromium plate (or even a dual micro-cracked chromium plate) of about 0.005 to 0.2 mil thickness. In general the upper layer of nickel should o be thinner than the lower layer (the preferred ratio is from 50:50 to 80:20 for obtaining the highest ductility of the composite as needed, for example on bumpers) and the intermediate layer should 'be the thinnest of the three plates. If ductility is not of great importance, then the lower layer may be thinner than the upper layer, for example a 46:60 ratio, 'and still obtain excellent Ycorrosion protection of the basis metal. For less severe exposure, the lower and upper layers may be'only 0.15 mils thick, and still obtain improved corrosion protection. Small percentages of other impurities besides sulfur may be present in the plates, for example, carbon, selenium, tellurium, zinc, cadmium and iron, and very appreciable quantities of cobalt, up to 50% cobalt, may be presentin the intermediate and upper layers of nickel'. The lower plate should, however, be as pure nickel as possible.

Thus, the lower nickel plate should be from a Wattstype nickel, as shown in Example l, or a fluoborate, high chloride, or sulfamate nickel plating bath, or a sulfurfrree semi-bright nickel plating bath, as shown in Example 2. The intermediate nickel plate can be from these same types of baths or even an -alkaline nickel bath, or a high content sodium, ammonium, lithium or magnesium type nickel bath, land should preferably have dissolved in the bath, sodium benzene sulnate, or sodium p-toluene sullinate in a concentration of about 0.1 to l gram/liter. Other compounds with a sulfur atom of valence less than plus six can be used to give a sulfur content to the intermediate nickel plate of about 0.05 to about 0.3% preferably about 0.08 to about 0.2%. For example, the following sulfur containing compounds in concentrations of about 0.004 to about 0.1 gram/liter can be employed: Sodium thiosulfate, sodium bisulite or suliite, sodium 'hyposultite or hydrosullite, sodium formaldehyde sulfoxylate, though sodium benzene suliinate, sodium toluene sulnates, Vsodium naphthalene sulinates, sodium chlorobenzene sullinate, sodium bromobenzene sulinate are Vthe best to use. In lien of the sodium salts, the potassium, lithium, zinc, magnesium, etc., salts may be used. Copper or lead salts should not be used because copper `and lead ions are known to be harmful impurities, even in traces, in nickel baths. Besides the above-mentioned inorganic and organic sulfur compounds containing a sulfur atom with less than plus six valence, other types can also be used, including sodium thiocyanate, phenyl sulfoxide, methyl sulfoxide, mercaptobenzoic acid, mercaptobenzenesulfonic acid, Vmercaptosuccinic acid, mer- Acaptobenzenealkane sulfonic acids, mercaptobenzene-oxyalkane sulfonic acids, thioureas, isothioureas, thiohydantoms, and especially their alkane sulfonic derivatives such as isothiourea-S-propane sulfonic acid. With this latter list of compounds, it is best to use concentrations which range from-0.005 to about 0.05 gram/liter, though when sulfonic groups 'are also present in the molecule, even 0.5 to l gram/liter concentrations may be used. For example, with thiourea only 0.005 to 0.04 gram/liter lshould be used as this is one of the most critical materials to use since an excess produces very brittle, poorly adherent plate, whereas the alkane sulfonic derivatives of the .isothiourea form are not very critical and can be used in concentrations as high as 1 gram/liter. The 'sulnatea however, such as sodium benzene sulfinate or toluene sulfinate are the least critical with variations in concentration and the best of all to use and can be employed as already mentioned in concentrations of 0.1 to l gram/liter and even higher, and even though bright Yplate is obtained, the adhesion and ductility are excellent.

In conjunction with the above-mentioned sulfur compounds there may also be present in the bath for plating the intermediate layer, organic sulfon-compounds such as sulfonc acids, sulfonamides, sulfonimides, sulfonyl iluorides, sulfones. If just the organic sulfon-compounds such as o-benzyl sulmide, p-toluene sulfonamide, napthalene sulfonic acid (mono, di, and tri), benzene sulfonic acid (mono, di, Iand tri) etc., are present in the nickel bath used for plating the intermediate layer, then the maximum sulfur content obtained for the intermediate nickel layer is about 0.06 or 0.07%. This is true if a wetting agent such as sodium octyl or lauryl sulfate is also present in the bath. For example, With l5 grams/ liter of nickel benzene disulfonate present in a Watts bath, the sulfur content of the nickel plate is about 0.064%. With 8 grams/liter of naphthalene 1,5 disulfouic acid present in a Watts bath, the sulfur content is about 0.044%, and with 1 gram/liter of p-toluene sulfonamide, it is just about the same value, 0.045% sulfur. However, with 1 gram/liter of sodium benzene sulfinate, the sulfur content is about 0.17%. With 1 to 10 grams/liter of sodium thiosulfate present, the sulfur content is about 0.8% or about 2.3% as nickel sulde. This is too much sulfur, andthe plate is very brittle, and the lateral corrosion of the intermediate plate is too rapid. It is preferred that the sulfur content of the intermediate plate should range from about 0.05% to about 0.3%, with the optimum range at about 0.06% to about 0.2% sulfur. In general,

for the intermediate plate a Watts bath at a pH of about 2.5 to 4.5 with `one of the best materials, sodium benzene suliinate or sodium p-toluene sulnate present in a concentration of 0.1 to about 0.3 gram/liter is about the best and simplest baths to use for plating the intermediate layer of nickel, and actually only a 0.005 to about 0.05 mil thick plate is needed in this case. With sodium thiosulfate instead of the sulfinates, a low concentration of 0.01 to 0.03 gram/liter in the Watts bath must be maintained in the intermediate nickel plating bath to give comparable results, that is, sulfur contents in this case of about 0.08 to about 0.1%. The drag-out tank or tanks following a semi-bright nickel tank may be used for the intermediate layer plating by merely adding about 0.1

to 0.3 gram/liter of sodium benzene suliinate or 0.01 to 0.03 gram/liter of sodium thiosulfate and maintaining this concentration during continued plating, and using only about .one-half to about three minutes plating time at 30 to 40 amps/sq. ft.

The upper nickel may be from a bath similar -to the yones used for plating the intermediate layer except lower concentrations of the sulfur containing compounds would -be used. For decorative plate, the top nickel should be from a bright nickel plating bath that employs one of the organic sulfo-oxygen compounds illustrated in Table II -of U.S. 2,513,280 (July 4, 1950) and Table H of UB.

2,800,440 (July 23, 1957) and preferably used together with unsaturated compounds or amines to give leveling and brilliance. The unsaturated compounds such as those carrying oleiinic type bonds or yacetylenic bonds without 0.14% sulfur, but when oleinic or acetylenic compounds not containing amine groups are present with the same sulfo-oxygen organic compounds, then the sulfur in the plate is usually `around 0.03 to 0.06%. With the latter 'type of bright nickel, the intermediate plate need have only about 0.06% to about 0.1% sulfur to obtain excellent corrosion protection results.

Wetting agents may be present in the baths to prevent pitting, or air agitation may be used. Besides boric acid,

other .buffers may be used such as formic, citric, acetic,Y

iluoboric, etc. The temperature of the baths may be from room to at least F. and the pH valuesrfrom at least 1 to 6 for the acidic baths. The following examples illustrate plating baths which can be used for Plate thickess 1 to about 1.5 mils.

Intermediate plate: Lower plate bath modified to include sodium thiosulfate concentration of 0.01 to 0.03 gram/ liter, temperature 30-60 C., pH 2.5, thickness of plate 0.005 to 0.2 mil.

Upper plate: Same ybath as for lower plate except that 2 grams/liter of one or more of the following are dissolved in the bath: p-toluene sulfonamide, o-benzoyl sulmide, benzene sulfonamide, naphthalene sulfonic acids, benzene sulfonic acids; thickness of plate 0.5 to 1.5 mils.

Example II (Tri-nickel plate) Lower plate:

NiSO4.6H2O grams/liter-- 200-400 INiCl2.6H2O do 30-60 H3BO3 -..dO

0.05 to 0.2 gram/liter of one or more of the following: bromal hydrate, chloral hydrate, formaldehyde, S-methoxy coumarin, coumarin, 3-chloro- Icoumarin. pH 3.0 to 5.5; temperature 3065 C. Plate thickness 0.15 to 1.5 mils.

Intermediate plate: Same bath as for lower plate or Watts bath of pH 2.5 to 4.2 with 0.1 to 0.3 gram/liter of sodium .benzene sulfinate or sodium thiosulfate in a concentration of 0.02 gram/liter; thickness of plate 0.005 to 0.1 mil.

Upper plate:

NiSO4.6H2O grams/liter 50-300 NiCl2.6I-I2O do 200-30 H3BO3 do 30-45 1 to 3 grams per liter of one or more of the following: o-benzoyl sulmide, p-toluene sulfonamide, benzene sulfonamide, naphthalene sulfonic acids, 2-hutyne 1,4-disulfonic acid, allyl sulfonic acid together with 0.1 to 0.3 gram/liter of 2-butyne 1,4- dioxyethanesulfo-nic acid. Thickness of plate `0.15 -to 1.5 mils. A ynal `bright chromium plate of 0.005 to 0.2 mil thickness.

Example 111 (Tri-nickel plate) Lower plate: Same as upper plate in Example II.

Intermediate plate: Same bath as for lower plate (or a Watts bath) with 0.1 to l gram/liter of sodium p-toluene sulnate or benzene sullinate (Na, K, Li, Mg or Zn salt); thickness of plate, 0.005 to 0.2 mil.

Upper plate: Same inorganic bath composition as given for upper plate in Example II and same organic sulfoncomposition, but containing 0.003 to 0.01 gram/liter of -N-allyl quinaldininm bromide; thickness of plate, 0.15 to 1.5 mils; a nal bright chromium plate of 0.005 to 0.2 mil thickness.

Example IV (Tri-nickel plate) Lower plate: Same as lower plate in Example II.

Intermediate plate: Watts nickel bath with 0.02 to 0.1 gram per liter of sodium bisulte with 0.005 to 0.3 gram/liter of sodium p-chlorobenzene sullinate, or sodium p-toluene suliinite, or sodium benzene sulnate. Thickness of plate 0.005 to 0.2 mil.

Upper plate: Same upper plate as in Example III.

The most ductile tri-nickel plate composites are those illustrated in Examples I, II and IV. Examples II, III and IV give very excellent results on copper plated steel and copper plated zinc die castings. Example I is primarily for non-decorative use where protection of the basis metal against marine or saline ty-pe exposure is practically the entire purpose. It could also be chromium plated. Example II illustrates the most ductile tri-nickel plate combination for decorative =use in servere outdoor exposure, and is very well suited for plating automobile bumpers.

What is claimed is:

1. A firmly bonded laminated corrosion-protective composite coating on a metal base susceptible to atmospheric corrosion comprising as its essential layers three adjacently bonded layers of electrodeposits, the lower layer of which `consists essentially of nickel electroplate having a thickness of about 0.15 mil to about 1.5 mils and an average sulfur content less than about 0.03%, the intermediate layer of which consists essentially of an electroplate selected from the group consisting of nickel electoplate and nickel-cobalt alloy electroplate containing at least about 50% nickel, said intermediate layer having a thickness of about 0.005 mil to about 0.2 mil and an average sulfure content -of about 0.05% to about 0.3%, and the upper layer of which consists essentially of an electroplate selected from the group consisting of nickel electroplate and nickel-cobalt alloy electroplate containing at least about 50% nickel, said upper layer having a thickness of about 0.15 mil to about 1.5 mils and an average sulfur content of about 0.02% to about 0.15%, said upper nickel plate containing a lower percentage of sulfur than `said intermediate nickel layer, and a higher percentage of sulfur than said lower layer.

2. A firmly bonded laminated corrosion-protective composite coating on a metal base of the group consisting of iron, steel, copper and its alloys, Zinc and its alloys, aluminum and its alloys, and magnesium and its alloys, comprising a three-layered nickel electrodeposit, the lower layer of which is a nickel electroplate having a thickness of about 0.15 mil to 1.5 mils and an average sulfur content less than about 0.03%, the intermediate layer of which is nickel electroplate having a thickness of about 0.005 mil to about 0.2 mil and an average sulfur content of about 0.05 to about 0.3%, and the upper layer of which is nickel electroplate having a thickness of about 0.2 to about 1.5 mils and an average sulfur content of about 0.02 to labout 0.15%, said upper nickel plate containing a lower percentage of sulfur than said intermediate nickel layer, and a higher percentage of sulfur than said lower layer.

3. A fmmly bonded ylaminated corrosion-protective composite coating on a metal base susceptible to atmospheric corrosion comprising essentially three adjacently bonded layers of clectrodeposits, the lower layer of which consists essentially of nickel electroplate having a thickness in the range of about 0.15 mil to about 1.5 mils and an average sulfur content less than about 0.03%, the intermediate layer of which consists essentially of an electroplate selected from the group consisting of nickel electroplate and a nickel-cobal alloy electroplate containing less than about 50% cobalt having a thickness of about 0.005 =mil to about 0.2 mil and an average sulfur content of about 0.05% to about 0.3%, and the upper layer of which consists essentially of an electroplate selected from the group consisting of nickel electroplate and nickelcobalt alloy electroplate containing less than about 50% cobalt having a thickness of about 0.15 mil to about 1.5 mils and an average sulfur content of -about 0.02% to about 0.15%, said upper nickel plate containing a lower percentage of sul-fur than said intermediate electroplate Aand a higher percentage of sulfur than said lower electroplate.

4. A coating in accordance with claim 1 wherein said lower layer of nickel is a semi-bright nickel electroplate which contains less than about 0.005% sulfur, said intermediate nickel layer is an electroplate which contains 0.06 4to about 0.2% sulfur, and said upper nickel layer is a bright nickel electroplate which contains 0.02 to -about 0.06% sulfur, said upper nickel plate containing a lower percentage of sulfur than said intermediate plate.

5. A coating in accordance with claim 1 wherein said upper nickel layer is electroplated with a chromium deposit of 0.005 to 0.2 mil thickness.

6. A coating in accordance with claim 2 wherein said upper nickel layer is electroplated with a chromium electrodeposit of 0.005 to 0.2 mil thickness.

7. A coating in accordance with clairn 3 wherein said upper bright nickel layer is electroplated with a bright chromium deposit of 0.005 to 0.2 mil thickness.

8. A coating in accordance with claim 2 "wherein said netal base is steel.

9. A method for electroplating from aqueous solutions ya corrosion-protective composite nickel coating comp-rising .as its essential layers three adjacently bonded layers of electrodeposits on a metal surface susceptible to atmospheric corrosion which comprises the steps of electroplating on said surface an adherent layer consisting essentially of nickel having a thickness of about 0.15 mil to 1.5 mils and an average sulfur content of less than about 0.03%, electroplating on said lower layer an adherent intermediate layer consisting essentially of an electroplate selected from the group consisting of nickel electroplate and nickelcobalt alloy electroplate containing at least about 50% nickel, said intermediate -layer having a thickness of about 0.005 to about 0.2 mill and anaverage sulfur content of about 0.05 to about 0.3 electroplating on -said inter-V mediate nickel layer an adherent upper layer consisting essentially of an electroplate selected from the group consisting of nickel electroplate and nickel-cobalt electroplate containing at least about 50% nickel, said upper layer having a thickness of about 0.2 to about 1.5 mils and an average sulfur content of 0.02 to 0.15%, said upper nickel layer containing a lower percentage of sulfur than said intermediate nickel layer, and a higher percentage of sulfur than said lower layer, each of said layers being electrodeposited in at least one electroplating step.

10. A method for electroplating from aqueous solutions a corrosion-protective composite three layered nickel vcoating on an industrial metal base of the group consisting of iron, steel, copper and its alloys, zinc and its alloys, aluminum and its alloys, and magnesium and its alloys, comprisin-g the steps of electroplatin-g on said surface an adherent lower layer of nickel having a thickness of about 0.15 mil to 1.5 mils and an average sulfur content less than about 0.03%, electroplating Von said *lower layer of nickel an adherent intermediate layer of nickel having a thickness of about 0.005 to about 0.2 mil and an'average sulfur content of 0.05% to 0.3%, electroplating on said intermediate nickel layer an upper nickel plate having a thickness of 0.15 to 1.5 mils and an average sulfur content of labout 0.02% to about 0.15%, said upper nickel plate containing a lower percentage of sulfur than said lintermediate nickel layer, an a higher percentage of sulfur than said lower layer.

l1. A method in accordance with claim 9 wherein said lower layer of nickel is plated `from an aqueous acidic semibright sulfur-free nickel plating bath, said intermediate nickel layer is plated from an aqueous acidic nickel bath containing I:from 0.004 to about 0.1 gram per liter sullites,V `and said upper nickel layer is plated from a bright nickel plating bath containing at least one organic sulfoncompound.

12. A method in accordance with claim 9' wherein said lower layer of nickel is plated from an aqueous acidic semibright sulfur-free nickel plating bath, said intermediate nickel layer is plated from an laqueous, acidic nickel bath containing from about-0.01m about 1 gram per liter of a compound selected from the :group `consisting of benzene suliinic lacid and substituted benzene sulnic acids, and said upper nickel layer is plated from a bright nickel plating bath containin-g yat Vleast one organic sulfon-compound.

13. A method in accordance with claim 11 wherein 4said upper bright nickel layer is electroplated with a Ibright chromium deposit of 0.005 to 0.2 mil thickness.

14. A method in accordance with claim 12 wherein said upper bright nickel layer is electroplated with a bright chromium deposit of 0.005 to 0.2 mil thickness.

15. A laminated corrosion protective composite coating on a metal base susceptible to atmospheric corrosion comprising as its essential layers three adjacently bonded layers of electrodeposits, the lowery layer thereof consisting essentially of nickel electroplate having a thickness of about 0.15 mil to about 1.5 mils and an average sulphur content less-than about 0.005%, the intermediate layer of said three layers consisting essentially of an electroplate selected from the group consisting of nickel electroplate and nickel-cobalt alloy electroplate containing at least about 50% nickel, said intermediate layer having a thickness of about 0.005 mil to about 0.2 mil and an average sulphur content of about 0.04% to about 0.18%, and the upper layer of said three layers consisting essentially of an electroplate selected from the group consisting of nickel electroplate and nickel-cobalt alloy electroplate containing at least about 50% nickel, said upper layer having -a thickness of ,about 0.15 mil to about 1.5 mils and an average sulphur content of about 0.02% to about 0.08%, said upper nickel plate containing a lower percent-age of sulphur than said intermediate nickel plate, and a higher percentage of sulphur than said lower nickel plate.

16. A laminated coating on a metal base in accordance with claim 15 wherein said upper nickel plate is electroplated with a chromium electrodeposit of 0.005 to 0.2 mil thickness.

17. A method ffor electroplating fromvaqueous solutions a corrosion protective composite coating on a metal surface susceptible to atmospheric corrosion which comprises the steps of (1) electroplating on said surface in at least one electroplating step an adherent layer consisting essentially of nickel having Ia thickness of about 0.15 mil to about 1.5 mils and an average sulphur content of less than about 0.03%, to thus dorm an adherent lower layer, (2) electroplating directly on said lower layer in at least one electroplating step an adherent intermediate layer consisting essentially of an electroplate selected from the group consisting of nickel electroplate and nickel-cobalt alloy electroplate containing at least about 50% nickel, said intermediate layer having a thickness of about 0.005 to about 0.2 mil and an average sulphur content of about 0.05 to about 0.3%, (3) electroplating directly on said intermediate nickel layer an adherent upper layer in at least one electroplating'step consisting essentially of an electroplate selected from the group consisting of nickel electroplate and nickel-cobalt alloy electroplate containing at least about 50% nickel, said upper layer having a thickness of about 0.2 to about 1.5 mils and an average sulphur content of 0.02% to 0.15%, said upper nickel layer containing a lower percentage of sulphur that said intermediate nickel layer, and a higher percentage of sulphur than said lower layer, said intermediate layer being plated from an aqueous acidic nickel bath containing 9 from about 0.004 to about 1 gram per liter of a bath soluble sulphur compound.

18. A method in accordance with claim 17 wherein said intermediate nickel layer is plated from an aqueous acidic nickel bath containing from about 0.004 to about 0.1 gram per liter of -a bath soluble sulphur compound selected `from the vgroup consisting of bath soluble thiosulphates, sulphites, bisulphites and hyposulphites.

19. A method in accordance with claim 17 wherein said intermediate nickel layer is plated from an aqueous acidic nickel bath containing about 0.01 to about l `gram/liter of Ia compound selected from the group consisting of benzene sulinic acid and substituted ybenzene sulnic acids.

References Cited in the le of this patent UNITED STATES PATENTS 

1. A FIRMLY BONDED LAMINATED CORROSION-PROTECTIVE COMPOSITE COATING ON A METAL BASE SUSCEPTIBLE TO ATMOSPHERIC CORROSION COMPRISING AS ITS ESSENTIAL LAYERS THEREE ADJACENTLY BONDED LAYERS OF ELECTRODEPOSITS, THE LOWER LAYER OF WHICH CONSISTS ESSENTIALLY OF NICKEL ELECTROPLATE HAVING A THICKNESS OF ABOUT 0.15 MIL TO ABOUT 1.5 MILS AND AN AVERAGE SULFUR CONTENT LESS THAN ABOUT 0.03%, THE INTERMEDIATE LAYER OF WHICH CONSISTS ESSENTIALLY OF AN ELECTROPLATE SELECTED FROM THE GROUP CONSISTING OF NICKEL ELECTOPLATE AND NICKEL-COBALT ALLOY ELECTROPLATE CONTAINING AT LEAST ABOUT 50% NICKEL, SAID INTERMEDIATE LAYER HAVING A THICKNESS OF ABOUT 0.005 MIL TO ABOUT 0.2 MIL AND AN AVERAGE SULFURE CONTENT OF ABOUT 0.05% TO ABOUT 0,3%, AND THE UPPER LAYER OF WHICH CONSISTS ESSENTIALLY OF AN ELECTROPLATE SELECTED FROM THE GROUP CONSISTING OF NICKEL ELECTROPLATE AND NICKEL-COBALT ALLOY ELECTROPLATE CONTAINING AT LEAST ABOUT 50% NICKEL, SAID UPPER LAYER HAVING A THICKNESS OF ABOUT 0.15 MIL TO ABOUT 1.5 MILS AND AN AVERAGE SULFUR CONTENT OF ABOUT 0.025% TO ABOUT 0.15%, SAID UPPER NICKEL PLATE CONTAINING A LOWER PERCENTAGE OF SULFUR THAN SAID INTERMEDIATE NCIKEL LAYER, AND A HIGHER PERCENTAGE OF SULFUR THAN SAID LOWER LAYER. 